1. Field of the Invention
The present invention relates to a sheet discharging apparatus. More specifically, the present invention relates to a sheet discharging apparatus mounted on a discharging side of an image forming apparatus such as a printer or a copying machine, which apparatus including wings for curving opposing sides of a sheet upward to increase stiffness, when a sheet discharged from the image forming apparatus is discharged to a large capacity tray. This operation of curving opposing sides of the sheet to increase stiffness will be hereinafter referred to as upward curving.
2. Description of the Background Art
On a sheet discharging side of an image forming apparatus such as a printer or a copying machine, a tray (also referred to as a "bin") for receiving the discharged sheet is mounted. Besides an ordinary tray on which several to several tens of sheets (relatively small number of sheets) are stacked, there is a large capacity tray which is capable of stacking and containing a large number of sheets of more than one hundred at one time. Some image forming apparatuses are provided with sorting function, by preparing a plurality of ordinary trays mentioned above on which a small number of sheets can be stacked at one time, moving upward/downward the trays in accordance with the timing of discharge of the sheets, and sorting the discharged sheets to prescribed trays. The sheet discharging apparatus includes one type or a plurality of types of such trays.
FIG. 9A shows an example of a conventional sheet discharging apparatus. The conventional sheet discharging apparatus includes a large capacity tray, and a tray group including a number of stages of trays for sorting. As shown in the figure, a conveyor 2 is provided at a central portion in height direction on one side of an approximately rectangular body 1 of the apparatus. On a side of body 1 opposing to conveyor 2, a container 3 for receiving the discharged sheet is provided. The image forming apparatus (not shown) is arranged on the side of conveyor 2.
Conveyor 2 receives a sheet on which an image is formed by the image forming apparatus, conveys the sheet over a conveying surface 4 and discharges the sheet to container 3. The sheet conveying force is applied, in a copying machine, for example, by pinching the sheet from above and below by a pair of upper and lower discharge rollers provided near a discharge outlet and by rotating the rollers, so that the sheet is conveyed forward in the conveying direction. In a printer, it is possible that printing ink on the sheet is not yet dried. Therefore, a vacuum conveyor (suction belt) is used, whereby the sheet is conveyed with the conveyor touching only the non-printed surface of the sheet.
FIG. 9B is a front view of conveyor 2 viewed from the direction of the arrow IXB in FIG. 9A. Referring to FIG. 9B, a pair of wings 5 are provided at opposing edges near a discharging outlet of conveyor 2. Wings 5 are reciprocal between a first position where each wing protrudes upward from conveying surface 4 as represented by the solid line in FIG. 9B, and a second position where each wing is positioned below conveying surface 4 as represented by two-dotted chain in FIG. 9B. Specifically, wings 5 are arranged parallel to each other along the conveying direction, and adapted to be movable between the two positions mentioned above with opposing edges of the wings serving as rotation axes 5a for forward/rearward rotation. A solenoid 6 is provided as a driving source for the movement.
Solenoid 6 is coupled near an outer side at a bottom surface of wing 5 (an edge opposing to the center of rotation), and solenoid 6 is conducted, so that the outer side of wing 5 is urged upward and rotated about rotation axis 5a to be placed at the first position. By stopping conduction to solenoid 6, wing 5 is rotated in the opposite direction and placed at the second position.
When wing 5 is at the first position, an upper surface 5b of wing 5 provides an inclined surface which gradually rises in the outer and forward direction of conveying. When it is at the second position, the upper surface is horizontal and approximately flush with conveying surface 4. Upper surface 5b of wing 5 is adapted to be in contact with lower side surface of the sheet moving on conveying surface 4.
Accordingly, when wings 5 are at the first position, opposing edges of the sheet in the proceeding direction are lifted along the upper surfaces 5b of wings 5, that is, subjected to the upward curving, and the sheet is maintained in a state extending straight along the proceeding direction. In other words, the discharged sheet would never be bent at an intermediate portion in the proceeding direction with the front portion hanging loose downward. Further, since the sheet is discharged diagonally upward, the sheet can fly over a relatively long distance. When wings 5 are at the second position, the sheet is kept flat and not subjected to upward curving, and is discharged in horizontal direction.
Container 3 includes trays (bins) 7 allowing stacking of a small number of sheets arranged in multiple stages, and a large capacity tray 8 containing a large number of sheets. Trays 7 are provided inclined with the front side in sheet conveying direction raised upward, and the trays 7 are arranged aligned in vertical direction spaced by a prescribed distance from each other. Trays 7 can be elevated/lowered collectively by an elevating apparatus in body 1.
Large capacity tray 8 is made relatively deep so as to increase capacity, and has sidewalls 8a on opposing edges and a stop wall 8b erected in front. When large capacity tray 8 is used, the actual position of receiving the sheet is lower by a prescribed distance from the sheet discharging position. Therefore, the discharged sheet drops by this distance and stacked. Therefore, wings 5 are set at the first position so that the sheet is curved upward and discharged diagonally upward. Thus the discharged sheet never has its forward portion bent and discharged downward, but the sheet flies over a relatively long distance in a straight extended state. The sheet abuts stop wall 8b and guided by sidewalls 8a, so that the number of sheets are successively stack in large capacity tray 8.
When sheets are to be stacked on tray 7 of small capacity and wings 5 are kept at the first position, it becomes necessary to ensure large space between upper and lower trays 7, as the sheet is discharged with opposing edges raised, which results in the apparatus of larger size, or smaller number of mountable trays. Further, the sheet tends to fly relatively farther, and hence it is possible that the sheet goes out from the front side of tray 7. Therefore, wings 5 are set to the second position so that the sheet is discharged flat. This enables reduction in space between the trays. Since only a small number of sheets are stacked in tray 7, the distance from the sheet discharging outlet to the receiving surface of tray 7 is short. Therefore, even when the sheet is discharged in the horizontal direction without upward curving, sheets can be stacked neatly on tray 7. In this manner, conduction to solenoid 6 is controlled in accordance with the tray used, and wings 5 are set to the desired state.
FIGS. 10A and 10B show another example of the conventional sheet discharging apparatus in which a large capacity tray 8' has a function of wings. More specifically, large capacity tray 8' has wings 5' attached integrally on the side of sheet discharging outlet. Similar to wings 5 set at the first position shown in FIGS. 9A and 9B, each of the wings 5' provides an inclined surface gradually rising forward and outward along the conveying direction. When a sheet is conveyed, it is subjected to upward curving by upper ends of wings 5', and is contained in large capacity tray 8'. In such a structure, it is not necessary to elevate/lower wings 5' dependent on the tray used, so that the apparatus can be simplified and control is facilitated.
However, the conventional sheet discharging apparatus described above suffers from the following problem. When large capacity tray 8' is used, wings 5' are always used raised at the first position. As a result, if a sheet itself is sturdy as in the case of a thick sheet and opposing edges are raised, the central portion of the sheet tends to rise. When a vacuum conveyor is used as conveyor 2 and the rising force of the central portion of the sheet exceeds the vacuum attraction, the sheet would be away from the surface of the conveyor belt, and thus conveying force cannot be applied. When the sheet is pinched by a pair of upper and lower rolls, unnatural force may be applied to the sheet, resulting in undesirable bending.
In the structure shown in FIGS. 9A and 9B, control for conducting/shutting power to solenoid 6 dependent on the state of use is necessary, which control is complicated. Further, upward/downward movement of wings 5 is realized by an electric mechanism including solenoid 6 and conducting apparatus therefor. Accordingly, a space for the electric mechanism is necessary and cost increases. Further, there is a possibility of malfunction in the control system, which may lead to a failure.
In the structure shown in FIGS. 10A and 10B, large capacity tray 8' must be mounted protruding in the direction of sheet discharge by the thickness of wings 5' (thickness of the wings in the discharging direction), which results in increased size of the whole apparatus.